Related question: Would there need to be two available seats for a 2-person itinerary to clear the waitlist? Or will it clear one pax if one seat is available? If the former, then would it make sense to split the reservation?
Yes, two would need to be available at the same time to clear prior to the gate.
Spitting the reservation increases the likelihood of at least one clearing. It also makes it possible for one person to clear and the other person not to clear, which some pax don't want, and it can mess up elite benefits.